Add data plane tests for serverless index

[rohanshah18]

Problem

Not all of the dataplane operations for serverless index are covered as a part of current test suite.

Solution

Add integration and error tests for data plane operations for serverless index. As a part of this PR, I have added:

1. Error tests for query and upsert data plane operations.
2. Integration tests for all data plane operations for both async and blocking stubs.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Infrastructure change (CI configs, etc)
• Non-code change (docs, etc)
• None of the above:
  Added more tests

Test Plan

Ran integration tests locally and on CI

[austin-denoble]

Thanks for adding additional data plane tests, these look good to me. However, I'm confused about the mocking in integration tests.